Wisconsin students' reading and math scores remained flat in the latest assessment known as the Nation's Report Card.

In most cases, Wisconsin students performed better than the national average, with 35% to 42% of students deemed proficient or above, depending on the subject and grade level.

But the state's largest district, Milwaukee Public Schools, continues to struggle, scoring well below state averages and behind almost every other large urban district tested.

And significant gaps persist in academic performance among students along racial, socioeconomic and other lines throughout the state.

Outgoing MPS Superintendent Darienne Driver said she was disappointed in the overall results for MPS, where proficiency rates were on average 12% to 15%.

"It is unacceptable that our students, especially our students of color, are, for the most part, scoring below state and national levels," Driver said in a news release after the 2017 National Assessment of Educational Progress, or NAEP, results were published last week.

Superintendent of Public Instruction and gubernatorial candidate Tony Evers voiced concern over the disparities in achievement and what he called "opportunity gaps for our kids."

"As our population continues to diversify, we cannot afford to leave large numbers of our students behind their peers and expect the Wisconsin economy to continue without disruption," Evers said.

The biennial Report Card and its companion Trial Urban District Assessment measure math and reading performance of fouth- and eighth-graders across the country, including those in 27 urban districts. MPS briefly suspended its participation and appears for the first time since 2013.

Here is a snapshot of the Wisconsin and Milwaukee results:

Among fourth-graders in Wisconsin, 35% of students were proficient or above in reading and 42% in math. Those are just below the national average in reading (37%) and just above the national average for math (40%).

For eighth-graders, 39% were proficient or above in reading and 38% in math, both above the national averages of 36% and 33%, respectively.

In MPS, 15% of students were proficient or above in fourth-grade reading and math and eighth-grade reading; 12% were proficient or above in eighth-grade math.

Among the 27 urban districts, MPS' overall scores were the second-lowest, behind Detroit, in fourth-grade math and reading, and eighth-grade math. It scored above Detroit and Cleveland in eighth-grade reading.

MPS' scores for eighth-grade math and fourth-grade reading were among the lowest of the 27 urban districts.

Achievement gaps were apparent throughout the state. In MPS, for example, 41% of white fourth-graders were proficient or above in math, compared with 7% of their black peers. For fourth-graders statewide, 49% of white students were proficient or above in math, compared with 11% of their black peers.